The Nakano Formation of the Oligocene Sakurae Group around the Yato River in the Shimane Prefecture,SW Japan,is divided into lower and upper parts which are correlated with the Kawado Tuff and Tazu Welded Tuff Members,respectively.The KawadoTuff Member is mainly composed of crystal tuff and contains intercalated rhyolite and andesite lavas.Consequently,this member could have been produced by a variety of eruption type.However,the Tazu Welded Tuff Member is charactenzed by a thick and widely distributed welded tuff,suggesting it was the production of a catastrophic eruption.